1. Field of the Invention
The present invention relates to a feeding mechanism for feeding an optical pickup, a magnetic head or the like in the radial direction of a disk and, in particular, to a head feeding mechanism suitable for achieving a reduction in size.
2. Description of the Related Art
When recording on and/or reproducing information from a disk such as a CD (compact disk), an MD (mini disk), an FD (floppy disk) or the like by using an optical pickup, a magnetic head or the like, it is necessary to feed the optical pickup, the magnetic head or the like in the radial direction of the disk. FIG. 6 shows a conventionally known head feeding mechanism.
In FIG. 6, numeral 1 indicates a carriage for an optical pickup (head) P including an objective lens 2, the carriage 1 being arranged between a guide shaft 3 and a screw shaft 4. The guide shaft 3 and the screw shaft 4 are arranged parallel and opposed to each other, and the screw shaft 4 is rotated in the normal and reverse directions by a thread motor M. On either side surface of the carriage, there protrude receiving portions 1a and 1b. One receiving portion 1a abuts the peripheral surface of the guide shaft 3, and the other receiving portions 1b are engaged by the screw shaft 4. Further, a plate spring 5 is fastened to the carriage 1 by a screw, and this plate spring 5 extends in a direction perpendicular to the axis of the screw shaft 4. A half nut 6 formed of synthetic resin and having a U-shaped cross-sectional shape is mounted to the forward end of the plate spring 5, and a female screw formed in the semi-cylindrical inner peripheral surface of the half nut 6 is held in pressing contact with the male screw of the screw shaft 4 and in mesh therewith due to the elastic force of the plate spring 5.
In the optical pickup feeding mechanism, generally constructed as described above, when the screw shaft 4 is rotated by the thread motor M in either the normal or the reverse direction, the torque is converted to a linear movement by the half nut 6, and transmitted to the carriage 1, so that the carriage 1, supporting the half nut 6 through the intermediation of the plate spring 5, moves in the axial direction of the guide shaft 3 and the screw shaft 4, whereby the entire optical pickup P is fed in the radial direction (to the inner or outer periphery) of the disk (not shown) to perform recording on and/or reproduction of information from the disk.
In the conventional technique described above, the female screw formed in the semi-cylindrical inner peripheral surface of the half nut 6 is held in pressing contact with the male screw of the screw shaft 4 due to the elastic force of the plate spring 5, whereby the torque of the screw shaft 4 is converted to a linear movement by the half nut 6 and transmitted to the carriage 1. Thus, the elastic biasing force of the plate spring 5 must be set to be larger than a certain level to ensure the engagement of the screw shaft 4 with the half nut 6. Thus, a relatively large torque is also required of the thread motor M, which is the drive source for the screw shaft 4.
Recently, there is a trend for in-car or portable CD players, MD players, floppy disk apparatuses and the like to be reduced in size. As a result, there is a demand for reducing the size of the thread motor, screw shaft, etc. used in the head feeding mechanism for the optical pickup, the magnetic head or the like. However, when a reduction in the size of the thread motor and the screw shaft is thus promoted, the torque of the thread motor is reduced, so that it is necessary to set the elastic biasing force of the plate spring, which holds the half nut in pressing contact with the screw shaft, to be small. Further, when the diameter of the screw shaft is reduced, the difference between the outer diameter and root diameter of the male screw formed on the outer peripheral surface of the screw shaft is reduced, and the difference between the inner diameter and root diameter of the female screw of the half nut is also inevitably reduced. For this reason, in the above-described conventional technique, when the size of the optical pickup feeding mechanism is reduced, it can happen that the female screw of the half nut moves over the male screw of the screw shaft due to vibration or the like transmitted from the exterior of the device. Or, due to the backlash required between the screws of the half nut and the screw shaft, the half nut is liable to move in the thrust direction of the screw shaft, resulting in a malfunction such as a dropout.
According to the present invention, there is provided a head feeding mechanism which includes a screw shaft adapted to rotate in the normal and reverse directions using a motor as a drive source, a nut member engaged with the screw shaft, and a spring member connected to a head and adapted to elastically press the nut member against the screw shaft and which causes the head to reciprocate in the thrust direction of the screw shaft through the intermediation of the nut member through rotation of the screw shaft, wherein the nut member has a substantially cylindrical female screw engaged with a male screw of the screw shaft, and wherein the nut member is elastically biased in both the radial direction and the thrust direction of the screw shaft by the spring member.
In this construction, if the elastic biasing force in the radial direction of the spring member, which holds the nut member in pressing contact with the screw shaft, is set to be small, there is no fear of the female screw of the nut member moving over the male screw of the screw shaft, so that a small torque suffices for the motor which rotates the screw shaft, which is effective in reducing the size of the motor and of the entire head feeding mechanism including this motor. Further, since the nut member is biased in the thrust direction of the screw shaft by the spring member, the thrust play of the nut member attributable to backlash is removed, and it is possible to prevent a malfunction such as a dropout from being generated by external vibration.
In the above-described construction, it is desirable to form on the spring member a joint portion to be held in pressing contact with the side surface of the nut member and an engagement portion to be engaged with the male screw of the screw shaft, and to elastically bias the nut member in the thrust direction of the screw shaft by the elastic force between the joint portion and the engagement portion. This makes it possible to reliably impart a biasing force in the thrust direction to the nut member with a simple construction.
In this case, it is desirable to provide the spring member with a first elastic arm extending to the screw shaft side using the head side as a stationary end, and a second elastic arm extending from the first elastic arm in the thrust direction of the screw shaft, and to form the joint portion on the free end side of the first elastic arm and form the engagement portion on the free end side of the second elastic arm. In this construction, it is possible to secure the requisite spring length of each of the first and second elastic arms, so that the elastic force which biases the nut member in the radial direction and the thrust direction of the screw shaft is easy to adjust, and it is possible to reduce variation in the elastic biasing force in each direction.